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Stabilisation of trans-1,2-dichloroethyleneRelated Patent Categories: Cleaning Compositions For Solid Surfaces, Auxiliary Compositions Therefor, Or Processes Of Preparing The Compositions, Cleaning Compositions Or Processes Of Preparing (e.g., Sodium Bisulfate Component, Etc.), For Cleaning A Specific Substrate Or Removing A Specific Contaminant (e.g., For Smoker`s Pipe, Etc.), For Printed Or Integrated Electrical Circuit, Or Semiconductor DeviceStabilisation of trans-1,2-dichloroethylene description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070032394, Stabilisation of trans-1,2-dichloroethylene. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to the stabilization of trans-1,2-dichloroethylene (TDCE) for the purpose of its use in the treatment of solid surfaces, more particularly for cleaning, degreasing, defluxing or drying metals. [0002] 1,2-Dichloroethylene is an industrial solvent widely used for the treatment of solid surfaces, for example for cleaning solid surfaces, degreasing metal components or defluxing printed circuits. [0003] 1,2-Dichloroethylene exists in two isomeric forms, cis-1,2-dichloroethylene and trans-1,2-dichloroethylene. The isomers of 1,2-dichloroethylene have distinct chemical and physical properties. In particular, the trans isomer has a lower boiling point, a lower density, a lower viscosity and a lower surface tension than those of the cis isomer. This is why trans-1,2-dichloroethylene (which will be denoted by TDCE) is the preferred isomer in solvent cleaning applications. The two isomers of 1,2-dichloroethylene can be separated by fractional distillation. However, during storage, TDCE is spontaneously converted to the cis isomer, unless it is stabilized, the cis isomer being more stable thermodynamically. U.S. Pat. No. 6,153,575 discloses the use of small amounts of aliphatic aldehyde hydrazones, optionally in combination with an epoxide, for inhibiting the isomerization of TDCE to the cis isomer during storage. [0004] The stability on storage of TDCE is its ability to withstand conversion or decomposition for a period which can range from several weeks to several months in conventional storage containers at a temperature which generally does not reach more than 50.degree. C. [0005] During its use as solvent for the treatment of solid surfaces, TDCE is subject to other attacks, related to the method of operation of the treatment equipment, which can result in its decomposition. The problems generated by the use of TDCE are therefore different from those encountered during storage. [0006] The main sources of attack on TDCE during its use, for example, in a device for degreasing metal components are: air, water, metals and heat. This is because metal degreasing is generally carried out by introducing the components to be degreased into an appropriate device above the liquid level of a tank containing the TDCE maintained at reflux. The TDCE vapours condense on the metal components and the condensate is repeatedly recycled. Under these conditions, the TDCE is subjected to various reactions, such as oxidation by the air, hydrolysis by the water originating from the condensation of atmospheric water vapour, thermal decomposition or catalytic reactions on contact with the metals. [0007] In the literature, various solutions have been provided for stabilizing some halogenated hydrocarbons confronted by the same sources of attack. The addition of various stabilizers is recommended in U.S. Pat. No. 3,043,888 for stabilizing halogenated hydrocarbons comprising from 1 to 3 carbons, more particularly trichloroethylene, during their use in metal degreasing. Some aldehyde hydrazones are particularly effective and can be used in combination with other compounds, such as aromatic compounds comprising a hydroxyl group, amines, organic epoxides, esters of monocarboxylic acids, alcohols or unsaturated compounds. Compounds which are especially effective in inhibiting the decomposition, catalysed by metals, of methylchloroform are described as being 1,3-dioxolane and its alkyl homologues or 1,4-dioxane (see U.S. Pat. No. 4,026,956; U.S. Pat. No. 3,251,891; U.S. Pat. No. 4,418,231 and U.S. Pat. No. 2,811,252). [0008] However, the solutions provided in the literature do not include a system for stabilizing a solvent, such as a halogenated hydrocarbon, combining all the characteristics required for a stabilizer, and in particular no complete system for stabilizing with respect to air, water, metals and heat is disclosed in the prior art for TDCE. [0009] First, the stabilizing system preferably has a two-fold action: a preventive action, more particularly in inhibiting side reactions, and a curative action, that is to say trapping in situ an undesirable effect. Subsequently, to facilitate the use of the stabilized solvent, the stabilizing system advantageously has a boiling point similar to that of the solvent, it is advantageously present in the liquid phase and in the vapour phase, it is insoluble or only slightly soluble in water and it preferably does not modify the properties of the solvent. In order not to modify the labelling of the solvent relating to the dangers of use, the stabilizing formulation is advantageously nontoxic. Finally, for economic reasons, the stabilizing formulation is preferably composed of inexpensive industrial products. [0010] It has now been found that the addition to the TDCE of several additives each having a role, such as acid acceptor, radical scavenger, Lewis base or compound possessing a buffering effect, constitutes a stabilizing system fully meeting the criteria mentioned above and makes it possible to obtain a stabilized TDCE solution which demonstrates good resistance to decomposition during its use in the treatment of metals. [0011] During the prolonged use under hot conditions of the same TDCE feedstock, atmospheric moisture, greases, oils, dirt and fine metallic particles, in particular when the metal components are composed of aluminium or of iron, accumulate in the TDCE and are the source of various reactions which result in the decomposition of the TDCE. This is because TDCE, because of its chemical structure, can undergo mainly three types of reactivity, which are the opening of the double bond, the reactivity of the doublet of the chlorine and the production of radicals. The decomposition of TDCE generally results in the formation of hydrochloric acid or of radicals. In the presence of metals, more particularly in the presence of aluminium or of iron, hydrochloric acid can react to form aluminium chloride (AlCl.sub.3) or ferric chloride (FeCl.sub.3), which are in addition catalysts of the exothermic condensation reaction of TDCE. The addition of stabilizing agents, such as acid acceptors, radical scavengers, Lewis bases or buffering agents, makes it possible to have a preventive and/or curative action with regard to these various reactions. [0012] A subject-matter of the invention is thus a stabilized solution of trans-1,2-dichloroethylene (TDCE) comprising, as additives, at least one acid acceptor, at least one radical scavenger, at least one Lewis base and at least one compound possessing a buffering effect. [0013] Mention may more particularly be made, among the acid acceptors which can be used in the stabilized solution according to the invention, of organic epoxides. Mention may be made, as nonlimiting examples, of ethylene oxide, propylene oxide, butylene oxide, butadiene monoxide, butadiene dioxide, epichlorohydrin, glycidol, isobutylene oxide or isopropyl glycidyl ether. Use will preferably be made of propylene oxide, butylene oxide or isopropyl glycidyl ether. [0014] In the context of the present invention, use may be made, as radical scavengers, of various organic compounds, such as alkenes, heterocycles or phenol derivatives. Mention may be made, as nonlimiting examples of alkenes, of diisobutylene, amylene, isoprene or .alpha.-methylstyrene. Mention may be made, as nonlimiting examples of heterocycles, of pyrroles, more particularly N-methylpyrrole, 1,4-dioxane or furans, more particularly tetrahydrofuran. Mention may be made, as nonlimiting examples of phenol derivatives, of phenol, thymol or ionol. [0015] It would not be departing from the scope of the present invention to use a first radical scavenger for the vapour phase and a second radical scavenger for the liquid phase. For example, isoprene can be used as radical scavenger for the vapour phase and diisobutylene as radical scavenger for the liquid phase. This combination of two scavengers has the advantage of being simultaneously effective with regard to the liquid TDCE and with regard to the vapour TDCE, which is necessary for the application envisaged. [0016] The Lewis bases, compounds which donate electron pairs, make it possible to saturate the Lewis acid sites of the metals and thus to inhibit the reaction for the formation of AlCl.sub.3 or FeCl.sub.3. The Lewis bases which can be used in the stabilized solution according to the invention are highly varied in nature. Mention may be made of acetals, ketones, nitro compounds, esters of carboxylic acids or ethers. Methylal will be preferred as acetals. Mention may be made, as nonlimiting examples of ketones, of acetone and methyl ethyl ketone. Mention may be made, as nonlimiting examples of nitro compounds, of nitromethane or nitroethane. Mention may be made, as nonlimiting examples of esters of carboxylic acids, of methyl formate, methyl acetate or isopropyl acetate. tert-Butyl methyl ether will be preferred as ether. [0017] Amines are more particularly suitable among the compounds possessing a buffering effect which can be used in the present invention. Amines make it possible to obtain a pH which is sufficiently basic to limit the kinetics of decomposition of the solvent and to maintain a relatively constant pH. Any amine may be used and use will preferably be made of triethylamine, N-methylmorpholine, diethylamine or N,N-diisopropylamine. [0018] It would not be departing from the scope of the invention to use, in addition to the compounds mentioned above, an alcohol to block AlCl.sub.3 or FeCl.sub.3 after their possible formation. The alcohols which may be suitable are, for example, methanol, ethanol, n-butanol or tert-butanol. [0019] Generally, the additives present in a stabilizing system have a boiling point in the vicinity of that of TDCE. However, compounds which are slightly less volatile than TDCE can be chosen which make it possible to specifically stabilize the liquid phase of TDCE or, conversely, more volatile compounds can be chosen in order to effectively stabilize the vapour phase of TDCE. [0020] The amount of each of the additives present in a stabilized solution of TDCE can vary greatly but the content of each additive in the stabilized solution will preferably be between 10 and 10 000 ppm, preferably between 10 and 1 000 ppm. The total amount of additives should be sufficient to inhibit the decomposition of TDCE under the usual conditions of use for the treatment of metals, without detrimentally affecting the properties of the solvent. It is considered that an overall content of additives of less than 50 000 ppm and preferably of less than 5 000 ppm makes it possible to obtain a stable TDCE solution which is simultaneously effective in the treatment of metals and the most economic possible. [0021] More particularly, a stabilized solution comprises from 200 ppm to 800 ppm of an acid acceptor, from 100 to 700 ppm of a radical scavenger or of a mixture of radical scavengers, from 10 to 100 ppm of a Lewis base and from 10 to 50 ppm of a compound possessing a buffering effect. [0022] A stabilized solution of TDCE according to the invention comprises butylene oxide, diisobutylene, isoprene, acetone and diethylamine. More particularly, the stabilized solution comprises from 200 ppm to 800 ppm, preferably 530 ppm, of butylene oxide, from 50 to 500 ppm, preferably 200 ppm, of diisobutylene, from 50 to 200 ppm, preferably 100 ppm, of isoprene, from 10 to 100 ppm, preferably 50 ppm, of acetone and from 10 to 50 ppm, preferably 10 ppm, of diethylamine. [0023] Experimental Part [0024] Various tests, the principles of which are set out below, are used to evaluate the effectiveness of the stabilization of TDCE: Continue reading about Stabilisation of trans-1,2-dichloroethylene... Full patent description for Stabilisation of trans-1,2-dichloroethylene Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Stabilisation of trans-1,2-dichloroethylene patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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